The centerpiece of the American missile defense system deployed by the Bush administration is the ground-based interceptor.

These missiles are now in silos at Vandenberg Air Force Base in California and at Fort Greely in Alaska. They have cost billions of dollars and are designed to intercept intercontinental ballistic missiles carrying nuclear warheads, launched possibly from North Korea or Iran.

But this is a highly controversial weapon system, and there is no certainty for all the money spent that these missiles will actually work.

Fort Greely is about 100 miles south of Fairbanks, Alaska, and not far from the magnificent peaks of the Alaska Range. The base was little more than an airstrip during World War II. During the Cold War, the U.S. military trained here for winter operations against the Soviet Union.

It almost closed in the 1990s, but when President Bush took office eight years ago, Fort Greely was in for a resurrection of sorts. Because of its position on the globe and the geometry of missile flights, Fort Greely was perfectly situated to house the ground-based interceptor — the key component of the U.S. missile defense system.

Growing The Missile Fields

There are several missile fields in Fort Greely that are either completed or under construction.

"Off to the far left, you see missile field three, where we have 20 silos," says Col. George Bond, the lead officer from the Pentagon's Missile Defense Agency. "By the time we complete the missile field in 2010, there will be 40 silos."

The missiles are housed below ground in silos, covered over by steel clamshell-shaped hatches. The missile chamber is accessible by ladder.

The silos are temperature- and humidity-controlled to keep the missiles fueled and ready for launch.

"You'll see these yellow cables are the umbilical cords that provide the data from our command launch equipment to give the missile its weapons task plan — basically the information it needs to launch and get on an interception path with the incoming warhead," Bond says.

There are three stages in the trajectory of a missile: the launch and initial ascent, called the boost phase; the mid-course, when the warhead is flying through space; and the terminal phase, when it re-enters the atmosphere and is heading toward the target.

The missiles at Fort Greely are mid-course interceptors, and Bond explains that they use an exoatmospheric kill vehicle, or EKV, to destroy the hostile warhead.

"It's 140 pounds. It contains absolutely no explosives, and it destroys an incoming warhead simply by kinetic energy," Bond says. "It's traveling at speeds [of] approximately 15,000 [miles] an hour, so at 140 pounds at those kind of speeds, it creates tremendous kinetic energy when it strikes the rocket."

'A Theology, Not A Technology'

These interceptors are on alert and ready for battle around-the-clock, every day. Control is in the hands of the 49th Missile Defense Battalion, a unit of the Alaska National Guard. Rotating squads of six soldiers operate the fire center full-time, and every day the squads go through training exercises designed to simulate an actual missile attack.

The Bush administration made the decision to deploy the missile defense system in a highly unorthodox way. Digging got under way on the silos, and the missiles were eventually placed in them before they went through a full set of flight tests to prove their capabilities.

That has given rise to sharp criticism. Earlier this year, Philip Coyle, who used to oversee weapons testing at the Pentagon and is now a specialist with the Center for Defense Information, testified on the current state of the missile defense system before a congressional panel.

"National missile defense has become a theology in the United States, not a technology," Coyle said. "As a result, U.S. missile defenses are being deployed without well-established operational criteria."

At the same hearing, Richard Garwin was even more scathing. Garwin has been a longtime adviser to the government on nuclear weapons, and was a member of the National Commission on Ballistic Missile Proliferation headed by Donald Rumsfeld in 1998.

Garwin told Congress that guarding the U.S. against nuclear attack will be a failure as long as the Pentagon attempts to carry it out using mid-course interceptors.

"Should a state be so misguided as to attempt to deliver nuclear weapons by ICBM, they could be guaranteed against intercept in mid-course by the use of appropriate countermeasures," Garwin said.

Debate Over Missile Systems And Efficacy

The issue of countermeasures is at the heart of the debate over missile defense — any missile that could deploy a nuclear warhead into space could also deploy countermeasures designed to fool an interceptor missile.

These countermeasures could be chaff creating a cloud around the warhead, or miniature jammers that would interfere with signals or balloons that look just like the warhead.

In space, the decoy and the real warhead travel at the same speed. Sensors in space, on the ground and on the kill vehicle itself have great difficulty determining which is the real threat.

But Lt. Gen. Henry Obering, director of the Missile Defense Agency, says the system has been tested using decoys.

"It has undergone six of nine successful intercept tests since 2000, and of course four of those have been against countermeasures," Obering says. "The testing that we've done is realistic from an operational perspective."

But the Missile Defense Agency will not provide more precise data on which countermeasures have actually been used in tests, leading critics like Joe Cirincione, president of the Ploughshares Fund, to be highly skeptical about Obering's claims.

"General Obering is misleading the Congress and the American public and the troops as to the capability of our systems," Cirincione says. "If we were to have a realistic test this year, next year, it would fail. It would fail catastrophically. And they know that, which is why they don't test that way."

Countering The Countermeasures

To confront the countermeasures problem, the Pentagon has invested heavily in new sensors and high-tech radar, like the sea-based X-band radar (SBX), a floating oil drilling platform with an enormous white bulb on its deck that houses one of the largest and most advanced radar platforms in the world.

Based in Alaska, it was recently in Hawaii for maintenance and tests. Its job is to track hostile missiles and provide data to the interceptors launched against them, says Jim Tinkham, the Missile Defense Agency specialist assigned to the SBX radar.

"Not only are we providing precision tracking, but we're starting to discriminate," Tinkham says. "We're starting to tell that's a piece of junk, this is a piece of junk, this is the target. This is what you're looking at. This is the bad guy."

The team that operates the SBX won't talk in detail about how well it can discriminate the junk from the real danger, but Ken Dube of Raytheon, the company that helped build the SBX radar, says the system is improving.

"We share the same concern," Dube says. "And to date in each of these sequential tests that we've conducted here with this national resource, we've met all the requirements of every test that we've accomplished to date."

Obering says the critics are wrong, but he does concede that dealing with countermeasures is an ongoing problem.

"There's a misconception that we cannot handle countermeasures," Obering says. "We cannot handle very complex countermeasures. I won't go into what that means, but there are things that an enemy can do to really try to confuse the system. Have we done everything we need to do? No. Have we done what we need to do based on the pace of our fielding and our deployment? The answer is yes."